The switch of the worst case on NBTI and hot-carrier reliability for 0.13 μm pMOSFETs

This investigation describes experiments on two sizes of p-channel metal-oxide-semiconductor field-effect-transistors (pMOSFETs), to study the negative bias temperature instability (NBTI) and hot-carrier (HC) induced degradation. This work demonstrates that the worst condition for pMOSFETs under HC tests occurs in CHC (channel HC, stressed at V_g = V_d) mode at high temperature. This study also shows that the worst degradation of pMOSFETs should occur in NBTI. This inference is based on a comparison of results for forward saturation current (I_ds,f) and reverse saturation current (I_ds,r) obtained in NBTI and HC tests.     

Proximity effect in the finite and incommensurate ferromagnet/superconductor systems

The original theory of a proximity effect is proposed for the bi- and tri-layered system ferromagnetic metal/superconductor (F/S) in dirty limit. The F₁/S/F₂ trilayer is examined more closely. The distinctions in materials, in thicknesses of F layers (d_f1 and d_f2), in parameters interfaces, and in local environments of layers are considered among the causes of incommensurability of trilayer. The peculiar T_c(d_f1, d_f2) interference pattern is predicted for the F₁/S/F₂ systems. The reentrant superconductivity and possibility of the better observability of the spin-valve regime are discussed.     

Fast and efficient VUV/UV emissions from (Ba,La)F2:Er crystals

We report observation of fast and efficient VUV/UV luminescence from the mixed (Ba,La)F₂:Er crystals. The broad bands, peaking at 162.5, 181.9, 194.2, 202.8, 216.1, 233.5 and 281.5 nm and decaying, at 10 and 293 K, with time constants of 46 and 35 ns respectively, are due to spin-allowed transitions from the low-spin (LS) state of the 4f¹⁰5d configuration.We also observed a weak and slow broad band emission peaking at 170 nm due to the spin-forbidden transition from the high-spin (HS) state of the 4f¹⁰5d configuration.While at room temperature the excitation into any of the three identified LS bands (J=8, 7 and 6) dominating the excitation spectrum yields fast VUV and UV emissions, at 10 K the excitation into higher lying J=7 and 6 bands generates slow and sharp line emissions. The positions of these lines fit energies of transitions originating from the ²G_7/2 multiplet at 66140 cm⁻¹. The emission from the ²G_7/2 multiplet has been never, to the best of our knowledge, observed before.The efficient and fast VUV and UV emissions from the higher (LS, J=8) with almost no contribution from the lower (HS, J=8) level of the 4f¹⁰5d configuration are possible because the modified crystal field in (Ba,La)F₂ shifts the level of the (LS, J=8) state below the ²F_5/2 multiplet which, therefore, does not contribute to nonradiative relaxation between the LS and HS levels.We conclude that the ²G_7/2 and ²F_5/2 levels have major impact on VUV and UV emissions from the Er³⁺ ion in (Ba,La)F₂ contributing to complex emission pattern described in this report Their key role, elucidated by the VUV and UV luminescence spectroscopy, is consistent with predictions from a simple configuration coordinate model based on experimental results and calculations of the 4f¹¹ energy levels.     

Vehicular traffic through a self-similar sequence of traffic lights

We study the dynamical behavior of vehicular traffic through a sequence of traffic lights positioned self-similarly on a highway, where all traffic lights turn on and off simultaneously with cycle time T_s. The signals are positioned self-similarly by Cantor set. The nonlinear-map model of vehicular traffic controlled by self-similar signals is presented. The vehicle exhibits the complex behavior with varying cycle time. The tour time is much lower such that signals are positioned periodically with the same interval. The arrival time T(x) at position x scales as (T(x)-x)∝x^d_f, where d_f is the fractal dimension of Cantor set. The landscape in the plot of T(x)−x against cycle time T_s shows a self-affine fractal with roughness exponent α=1−d_f.     

Thermal fluctuations in pinned elastic systems: field theory of rare events and droplets

Using the functional renormalization group (FRG) we study the thermal fluctuations of elastic objects (displacement field u, internal dimension d) pinned by a random potential at low temperature T, as prototypes for glasses. A challenge is how the field theory can describe both typical (minimum energy T = 0) configurations, as well as thermal averages which, at any non-zero T as in the phenomenological droplet picture, are dominated by rare degeneracies between low lying minima. We show that this occurs through an essentially non-perturbative thermal boundary layer (TBL) in the (running) effective action Γ [u] at T > 0 for which we find a consistent scaling ansatz to all orders. The TBL describes how temperature smoothes the singularities of the T = 0 theory and contains the physics of rare thermal excitations (droplets). The formal structure of this TBL, which involves all cumulants of the coarse grained disorder, is first explored around d = 4 using a one-loop Wilson RG. Next, a more systematic exact RG (ERG) method is employed, and first tested on d = 0 models where it can be pushed quite far. There we obtain precise relations between TBL quantities and droplet probabilities (those are constrained by exact identities which are then checked against recent exact results). Our analysis is then extended to higher d, where we illustrate how the TBL scaling remains consistent to all orders in the ERG and how droplet picture results can be retrieved. Since correlations are determined deep in the TBL (by derivatives of Γ [u] at u = 0), it remains to be understood (in any d) how they can be retrieved (as u = 0⁺ limits in the non-analytic T = 0 effective action), i.e., how to recover a T = 0 critical theory. This formidable “matching problem” is solved in detail for d = 0, N = 1 by studying the (partial) TBL structure of higher cumulants when points are brought together. We thereby obtain the β-function at T = 0, all ambiguities removed, displayed here up to four loops. A discussion of the d > 4 case and an exact solution at large d are also provided.     

The field theory approach to percolation processes

We review the field theory approach to percolation processes. Specifically, we focus on the so-called simple and general epidemic processes that display continuous non-equilibrium active to absorbing state phase transitions whose asymptotic features are governed, respectively, by the directed (DP) and dynamic isotropic percolation (dIP) universality classes. We discuss the construction of a field theory representation for these Markovian stochastic processes based on fundamental phenomenological considerations, as well as from a specific microscopic reaction-diffusion model realization. Subsequently we explain how dynamic renormalization group (RG) methods can be applied to obtain the universal properties near the critical point in an expansion about the upper critical dimensions d_c = 4 (DP) and 6 (dIP). We provide a detailed overview of results for critical exponents, scaling functions, crossover phenomena, finite-size scaling, and also briefly comment on the influence of long-range spreading, the presence of a boundary, multispecies generalizations, coupling of the order parameter to other conserved modes, and quenched disorder.     

Textural and electronic characteristics of mechanochemically activated composites with nanosilica and activated carbon

Nanosilicas (A-50, A-300, A-500)/activated carbon (AC, S_BET = 1520 m²/g) composites were prepared using short-term (5 min) mechanochemical activation (MCA) of powder mixtures in a microbreaker. Smaller silica nanoparticles of A-500 (average diameter d_av = 5.5 nm) can more easily penetrate into broad mesopores and macropores of AC microparticles than larger nanoparticles of A-50 (d_av = 52.4 nm) or A-300 (d_av = 8.1 nm). After MCA of silica/AC, nanopores of non-broken AC nanoparticles remained accessible for adsorbed N₂ molecules. According to ultra-soft X-ray emission spectra (USXES), MCA of silica/AC caused formation of chemical bonds Si-O-C; however, Si-C and Si-Si bonds were practically not formed. A decrease in intensity of OK_α band in respect to CK_α band of silica/AC composites with diminishing sizes of silica nanoparticles is due to both changes in the surface structure of particles and penetration of a greater number of silica nanoparticles into broad pores of AC microparticles and restriction of penetration depth of exciting electron beam into the AC particles.     

Critical exponents of the Ising model on low-dimensional fractal media

The critical behavior of the Ising model on fractal substrates with noninteger Hausdorff dimension d_H<2 and infinite ramification order is studied by means of the short-time critical dynamic scaling approach. Our determinations of the critical temperatures and critical exponents β, γ, and ν are compared to the predictions of the Wilson-Fisher expansion, the Wallace-Zia expansion, the transfer matrix method, and more recent Monte Carlo simulations using finite-size scaling analysis. We also determined the effective dimension (d_ef), which plays the role of the Euclidean dimension in the formulation of the dynamic scaling and in the hyperscaling relationship d_ef=2β/ν+γ/ν. Furthermore, we obtained the dynamic exponent z of the nonequilibrium correlation length and the exponent θ that governs the initial increase of the magnetization. Our results are consistent with the convergence of the lower-critical dimension towards d=1 for fractal substrates and suggest that the Hausdorff dimension may be different from the effective dimension.     

Standard and non-standard metarefraction with confocal lenslet arrays

A recent paper demonstrated that two lenslet arrays with focal lengths f₁ and f₂, separated by f₁+f₂, change the direction of transmitted light rays approximately like the interface between isotropic media with refractive indices n₁ and n₂, where n₁/n₂=-f₁/f₂ [J. Courtial, New J. Phys. 10 (2008) 083033]. This is true if light passes through corresponding lenslets, that is lenslets that share an optical axis. Light can also pass through different combinations of non-corresponding lenslets. Such light can be either absorbed or allowed to form “ghost images”; either way, it leads to a limitation of the field of view of confocal lenslet arrays. This paper describes, qualitatively and quantitatively, a number of such field-of-view limitations.     

Predominant factors affecting the dielectric and piezoelectric properties of bismuth-containing complex perovskite solid solution

To study the factors affecting the dielectric and piezoelectric properties of bismuth-containing complex perovskites, the solid solution (1−x)Pb(Mg_1/3Nb_2/3)O₃-xBi(Mg_2/3Nb_1/3)O₃ was prepared by the solid state reaction method and its dielectric and piezoelectric properties were investigated. It is found that (1) at room temperature, the nonlinearity of the DE-loop for Pb(Mg_1/3Nb_2/3)O₃ is completely suppressed at a rather low x (<5%); (2) dielectric constant versus temperature curves deviate from the Curie-Weiss law at a temperature T_d much higher than the dielectric constant peak temperature T_m and T_m−T_d decreases considerably with increasing x; and (3) frequency dispersion ΔT_m=T_m (1 MHz)−T_m (10 kHz) increases with increasing x. Possible factors responsible for the variation of the dielectric and piezoelectric properties with x are discussed.     

VUV spectroscopic properties of Ce and Pr-doped AREP2O7-type alkali rare earth diphosphates (A=Na, K, Rb, Cs; RE=Y, Lu)

Spectroscopic properties of Ce³⁺ and Pr³⁺-doped AREP₂O₇-type alkali rare earth diphosphates (A=Na, K, Rb, Cs; RE=Y, Lu) have been investigated using VUV spectroscopy technique. Ce³⁺-doped samples show typical Ce³⁺ emission in the range of 325-450 nm. The strong host absorption band starting at around 160 nm indicates that the optical band gap of AREP₂O₇ hosts is at least 7.7 eV, and the host→Ce³⁺ energy transfer process is rather efficient. However, AREP₂O₇:Pr³⁺ samples show less efficient host→Pr³⁺ energy transfer. The direct Pr³⁺ 4f²→4f¹5d¹ excitation, which are 12160±640 cm⁻¹ higher respect to that of Ce³⁺, leads to strong 4f¹5d¹→4f² emission bands in the range of 230-325 nm but no obvious 4f²→4f² emission lines.     

ESR spectra of Eu centers in defect Ga2S3 single crystals

In this paper, the author presents the results of measurements of the low-temperature and angular dependences of the ESR spectra of Eu²⁺ centers in defect Ga₂S₃ single crystals in the temperature range 8–29 K and for 0–180° orientations of the static magnetic field. The electron structure of impurity ¹⁵¹Eu atoms in Ga₂S₃:Eu single crystals has been studied by using the ESR method at different doping proportions of Eu atoms. Ga₂S₃ single crystals were grown from the melt using the Bridgman method. The Eu concentration was determined by atomic absorption analysis and X–ray fluorescence analysis (XRFA). By investigation on the ESR spectra, the author has first determined the values of charge states for Eu, which have turned out to be a Eu²⁺(4f⁷) ion with spin S=7/2, g=4.18±0.02 and concentration of the states of Eu N=6.3×10¹⁴ cm⁻³.     

XPS and thermomagnetic characterization of the CeNi4Cr compound

The magnetic, thermodynamic and electronic structure properties are discussed for the CeNi₄Cr compound. The X-ray photoemission spectra (XPS) provide an evidence of a mixed valence behavior with the occupancy of the f states n_f=0.89 and their hybridization with the conduction electrons Δ=30 meV. These values reproduce well the magnetic susceptibility χ(T=0), which is enhanced compared to similar CeNi₄M (M=Al, B, Cu) compounds. In combination with a slightly increased electronic specific heat coefficient (up to 100 mJ mol⁻¹ K⁻²), this compound can be classified as being on the border of the heavy fermion and mixed valence behavior. Using a small magnetic field in the χ(T) measurements reveals a presence of magnetically ordered impurity phase, which is easily damped by higher fields and it is shown that the contribution of this phase is minor. The question of the dependence of the electronic specific heat coefficient on the magnetic field is also addressed and the observations agree well with theoretical predictions based on the Anderson model.     

Optical and magnetic properties of laser-deposited Co-doped ZnO thin films

We report the optical and magnetic properties of laser-deposited Zn_1−xCo_xO (x=0.06-0.3) thin films with no intentional electrical carrier doping. The analysis of the high-temperature magnetization data provides an unambiguous evidence that antiferromagnetic superexchange interaction is the dominant mechanism of the exchange coupling between Co ions in Zn_1−xCo_xO alloy, yielding the value of the effective exchange integral J₁/k_B to be about −27 K. The low-temperature magnetization data reveals a spin glass transition in Zn_1−xCo_xO alloy for the Co content x>0.15, giving the value of the spin freezing temperature T_f to be ∼8 and ∼12 K for x=0.2 and 0.25, respectively. Optical spectra analysis shows a linear increase of the band gap E_g with the increase of the Co content following E_g=3.231+1.144x eV.     

Tunneling magnetoresistance in exchange-biased CoFeB/AlOx/Co/IrMn junctions

A series of exchange-biased magnetic tunneling junctions (MTJs) were made in an in-plane deposition field (h) = 500 Oe. The deposition sequence was Si(1 0 0)/Ta(30 Å)/CoFeB(75 Å)/AlO_x(d Å)/Co(75 Å)/IrMn(90 Å)/Ta(100 Å), where d was varied from 12 Å to 30 Å. The MTJ was formed by the cross-strip method with a junction area of 0.0225 mm². The tunneling magnetoresistance (ΔR/R) of each MTJ was measured. The high-resolution cross-sectional transmission electron microscopic (HR X-TEM) image shows the very smooth interface and clear microstructure. X-ray diffraction (XRD) demonstrates that the IrMn layer of the MTJ exhibits a (1 1 1) texture. From the results (ΔR/R) increases from 17% to 50%, as d increases from 12 Å to 30 Å. The tunneling resistance (R_o) of these junctions ranges from 150 Ω to 250 Ω. The exchange-biasing field (H_ex) of the MTJ is 50-95 Oe. Finally, the saturation resistance (R_s) was measured as a function of the angle (α) of rotation, where α is the angle between h and the in-plane saturation field (H_s) = 1.1 kOe. The following figure presents the dependence of R_s on α, instead of originally expected independence, the curve actually varies with a period of π.     

Synthesis and electrochemical characteristics of Ta-N thin films fabricated by cathodic arc deposition

Ta-N thin films were deposited on AISI 317L stainless steel (SS) substrates by cathodic arc deposition (CAD) at substrate biases of −50 and −200 V. The as-deposited films were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray analysis (EDX). The results show that stoichiometric TaN with hexagonal lattice (3 0 0) preferred orientation was achieved at the bias of −200 V. On the other hand, Ta-rich Ta-N thin film deposited at −50 V shows amorphous nature. According to the XPS result, Ta element in the films surface exist in bonded state, including the Ta-N bonds characterized by the doublet (Ta 4f_7/2 = 23.7 eV and Ta 4f_5/2 = 25.7 eV). Electrochemical properties of the Ta-N coated stainless steel systems were investigated using potentiodynamic polarization and electrochemical impedance spectroscope (EIS) in Hank's solution at 37 °C. For the Ta-N coated samples, the corrosion current (i_corr) is two or three orders of magnitude lower than that of the uncoated ones, indicating a significantly improved corrosion resistance. Growth defects in the Ta-N thin films produced by CAD, however, play a key role in the corrosion process, especially the localised corrosion. Using the polarization fitting and the EIS modelling, we compared the polarization resistance (R_p) and the porosity (P) of the Ta-N coatings deposited at different biases. It seems that Ta-N film with comparatively lower bias (−50 V) shows better corrosion behavior in artifical physiological solution. That may be attributed to the effect of ion bombarding, which can be modulated by the substrate bias.     

Very high field magnetization and AC susceptibility of native horse spleen ferritin

The magnetization of native horse spleen ferritin protein is measured in pulsed magnetic fields to 55 T at T=1.52 K. The magnetization rises smoothly with negative curvature due to uncompensated Fe³⁺ spins and with a large high field slope due to the underlying antiferromagnetic ferritin core. Even at highest fields the magnetic moment is only ∼4% of the saturation moment of the full complement of Fe³⁺ in the ferritin molecule. The AC magnetic susceptibility, χ_AC(T,f), responding to the uncompensated spins, reaches a maximum near the superparamagnetic blocking temperature with the temperature of the maximum, T_M, varying with excitation frequency, T_M⁻¹ α log f for 10?f?10⁴ Hz.     

Superconducting slab in contact with thin superconducting layer at higher critical temperature

Within the framework of nonlinear time dependent Ginzburg–Landau equations (TDGL) we study the properties of a mesoscopic superconducting film with both surfaces in contact with a thin superconducting layer at a higher critical temperature. The properties of the layer are taken into account by the de Gennes boundary conditions via the extrapolation length b. We assume that the magnetic field is parallel to the multilayer interfaces. We obtain magnetization curves and calculate the spatial distribution of the superconducting electron density using a numerical method based on the technique of gauge invariant variables. This work tests both the rectangular cross-section size and b limit for the occurrence of vortices in a mesoscopic sample of area d_xxd_y where d_y = 80ξ(0) and dx varies discretely from 20ξ(0) to 3ξ(0). Our data also show a linear behavior of the magnetization curve and a power-law of order parameter modulus in limit b → 0_-.